Bump xunit.runner.visualstudio from 2.5.7 to 2.8.1 (#581)

Bumps [xunit.runner.visualstudio](https://github.com/xunit/visualstudio.xunit) from 2.5.7 to 2.8.1.
- [Release notes](https://github.com/xunit/visualstudio.xunit/releases)
- [Commits](xunit/visualstudio.xunit@2.5.7...2.8.1)

---
updated-dependencies:
- dependency-name: xunit.runner.visualstudio
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

tests/ImageSort.UnitTests/ImageSort.UnitTests.csproj

@@ -18,7 +18,7 @@
     <PackageReference Include="ReactiveUI" Version="20.1.1" />
     <PackageReference Include="ReactiveUI.Testing" Version="20.1.1" />
     <PackageReference Include="xunit" Version="2.8.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.7">
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>

tests/ImageSort.WPF.UiTests/ImageSort.WPF.UiTests.csproj

@@ -10,7 +10,7 @@
     <PackageReference Include="FlaUI.UIA3" Version="4.0.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.10.0" />
     <PackageReference Include="xunit" Version="2.8.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.5.7">
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.8.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>